Outdoor unit resonator correction

ABSTRACT

A system comprises a microwave backhaul outdoor unit having a first resonant circuit, phase error determination circuitry, and phase error compensation circuitry. The first resonant circuit is operable to generate a first signal characterized by a first amount of phase noise and a first amount of temperature stability. The phase error determination circuitry is operable to generate a phase error signal indicative of phase error between the first signal and a second signal, wherein the second signal is characterized by a second amount of phase noise that is greater than the first amount of phase noise, and the second signal is characterized by a second amount of temperature instability that is less than the first amount of temperature instability. The phase error compensation circuitry is operable to adjust the phase of a data signal based on the phase error signal, the adjustment resulting in a phase compensated signal.

PRIORITY CLAIM

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/929,465 filed on Nov. 2, 2015 which claims priority to U.S.provisional patent application 62/075,297 filed on Nov. 5, 2014. Thisapplication also claim priority to Indian provisional patent application3615/DEL/2015 filed on Nov. 56, 2015. Each of the above referenceddocuments is hereby incorporated herein by reference in its entirety.

BACKGROUND

Limitations and disadvantages of conventional methods and systems formicrowave backhaul will become apparent to one of skill in the art,through comparison of such systems with some aspects of the presentinvention as set forth in the remainder of the present application withreference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Systems and methods are provided for low phase noise microwave backhaulcommunications, substantially as shown in and/or described in connectionwith at least one of the figures, as set forth more completely in theclaims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A shows an example split-architecture microwave backhaultransceiver, in accordance with aspects of this disclosure.

FIG. 1B shows an example all-outdoor microwave backhaul transceiver, inaccordance with aspects of this disclosure.

FIG. 2A shows an example split-architecture microwave backhaultransceiver, in accordance with aspects of this disclosure.

FIG. 2B shows an example all-outdoor microwave backhaul transceiver, inaccordance with aspects of this disclosure.

FIG. 2C shows a portion of an example microwave backhaul receivercomprising a feedback path, in accordance with aspects of thisdisclosure.

FIG. 3A is a flowchart illustrating an example process forlow-phase-noise reception by a microwave backhaul transceiver.

FIG. 3B is a flowchart illustrating an example process forlow-phase-noise transmission by a microwave backhaul transceiver.

FIG. 4 shows an example implementation of a portion of the transmit andreceive digital paths of FIGS. 1 and 2.

FIGS. 5A-5D show example implementations of the auxiliary reference PLLof FIGS. 1 and 2.

FIG. 6 shows a portion of an example microwave backhaul receiver, inaccordance with aspects of this disclosure.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “microwave” frequencies range from approximately 300 MHzto 300 GHz and “millimeter wave” frequencies range from approximately 30GHz to 300 GHz. Thus, the “microwave” band includes the “millimeterwave” band.

FIG. 1A shows an example split-architecture microwave backhaultransceiver, in accordance with aspects of this disclosure. The examplemicrowave backhaul transceiver is split into an outdoor unit 100 and anindoor unit 120.

The indoor unit 120 comprises an instance of intermediate frequency (IF)input and/or output interface 122, a multi-channel modulator and/ordemodulator (modem) 124, and an interface 126 (e.g., a serializationand/or deserialization circuit, gigabit Ethernet interface, and/or thelike).

The outdoor unit 100 comprises antennas 135 and 136 (in another exampleimplementation a single antenna may be shared through use of adiplexer), amplifier 133, a variable attenuator 132, receive analogfront-end circuit (AFE) 138, a digital receive path circuit 142, atransmit AFE 158, a digital transmit path circuit 154, an instance of IFinput and/or output interface 122 (called out as 122 a) a, a localoscillator (LO) synthesizer 182, and an auxiliary phase locked loop(PLL) 184. Also shown is a controller 104 (e.g., a state machine, aprogrammable interrupt controller, an ARM-based processor, or the like)which may be on-chip with the transceiver or may be on a separate chipin the ODU.

In an example implementation, the amplifier 133 and attenuator 132 maybe implemented on a GaAs die and the AFEs 138, 158 and digital circuitry142 and 154 may be implemented on a CMOS die. In another exampleimplementation, the amplifier 133 and attenuator 132 may be unnecessaryand the microwave transceiver 100 may be entirely CMOS, for example.

The receive AFE 138 comprises an amplifier 130, a mixer 132, a filter134, an analog-to-digital converter 136, and frequency synthesizer 140.The transmit AFE 158 comprises amplifier 166, mixer 164, filter 162, adigital-to-analog converter 160, and a frequency synthesizer 168.

For receive, the SAW or BAW-based oscillator signal 183 output bysynthesizer 182 is fed to frequency synthesizer 140 which generates theLO signal used by the mixer 132. The SAW or BAW-based oscillator signal183 is also fed to the auxiliary PLL 184 for generation of the errorsignal 185. The received microwave signal 129 is amplified by amplifier130 and downconverted to baseband by mixer 132. The baseband signal isthen filtered by filter 134 and digitized by ADC 136. The digitizedbaseband signal is then provided to the digital receive circuitry 142,where its phase is corrected based on error signal 185 before beingpassed to interface 122 a. Interface 122 a upconverts the basebandsignal to an IF signal which may comprise one or more channels selectedby digital receive circuitry 142, where the upconversion may includeperforming channel stacking where more than one channel is selected. Theinterface 122 b receives the IF signal carrying the channel(s), themodem 124 demodulates the channel(s), and the interface 126 processes(e.g., serializes, encapsulates, and/or the like) the demodulated datafor transmission to a destination of the data (e.g., a cellularbasestation).

For transmit, the interface 126 processes (e.g., deserializes,decapsulates, and/or the like) data received from a source (e.g.,cellular basestation) and passes the data to the modem 124 whichmodulates the data onto one or more channels. The modulated channel(s)is(are) then upconverted to IF by interface 122 b and sent over the link144 to the outdoor unit 100. In the outdoor unit 100, the SAW orBAW-based oscillator signal 183 output by synthesizer 182 is fed tofrequency synthesizer 168 which generates the LO signal used by themixer 164. The SAW or BAW-based oscillator signal 183 is also fed to theauxiliary PLL 184 for generation of the error signal 185. In the digitaltransmit circuitry 154, the phase of the baseband signal from theinterface 122 a is corrected (e.g., pre or post compensated) based onthe error signal 185. The phase-compensated signal is then converted toanalog by DAC 160, filtered by filter 162, upconverted by mixer 164, andamplified by amplifier 166 resulting in transmitted signal 167.

In FIG. 1A, the error signal 185 is generated by the auxiliary PLL 184using the XTAL-based oscillator signal 189. Example details of this aredescribed below with reference to FIGS. 5A-5C. The error signal 185 isalso provided to the synthesizer 182 for tuning the frequency of the SAWor BAW-based oscillator signal 183 (e.g., to compensate for drift due totemperature change).

FIG. 1B shows an example all-outdoor microwave backhaul transceiver, inaccordance with aspects of this disclosure. The implementation of FIG.1B is similar to the implementation of FIG. 1A with the difference beingthat modem 124 and interface 126 are integrated (e.g., in the samehousing, on the same printed circuit board, on the same semiconductordie, and/or otherwise) with the outdoor unit 100. The link 144 thenprovides connectivity to an external device 190 (e.g., another outdoorunit, an indoor unit, or other electronic device).

FIG. 2A shows an example split-architecture microwave backhaultransceiver, in accordance with aspects of this disclosure. FIG. 2A issubstantially the same as FIG. 1A, except the auxiliary PLL 184 receivesa reference signal 201 from the reference generator 128 of the indoorunit 120, rather than reference signal 189 from the crystal 188 shown inFIG. 1A. The reference signal 201 may, for example, be an analog tonepicked off of the link 144 by an analog band select filter. Thereference signal 201 may, for example, be digitized and then selected byinterface 122 a for conveyance to the auxiliary PLL 184.

FIG. 2B shows an example all-outdoor microwave backhaul transceiver, inaccordance with aspects of this disclosure. The implementation of FIG.2B is similar to the implementation of FIG. 2A. One difference in FIG.2A is that modem 124 and interface 126 are integrated (e.g., in the samehousing, on the same printed circuit board, on the same semiconductordie, and/or otherwise) with the outdoor unit 100. Another difference isthat there are two links 144A and 144B connecting the outdoor unit 100to external device(s). The outdoor unit 100 may, for example, sendand/or receive data to and/or from a first external device 190A (e.g.,another outdoor unit, an indoor unit, or other device) via the cable144A. The outdoor unit 100 may, for example, receive reference signal201 via link 144B data to and/or from a second external device 190B(e.g., another outdoor unit, an indoor unit, or other device). Where190A is another outdoor unit, it may be a split-architecture orall-outdoor architecture. When data and reference signal come from thesame external devise, the two links 144A and 144B can use differentphysical medium or the same physical medium.

FIG. 2C shows a portion of an example microwave backhaul receivercomprising a feedback path. The depicted portion of the microwavetransceiver 100 is similar to those described above but additionallycomprises a feedback receive path comprising attenuator 234, AFE 220,and digital portion 232. Portions of microwave transceiver 100 not shownin FIG. 2C may be as shown in any of FIGS. 1A, 1B, 2A, and 2B.

In operation, the output of amplifier 133 is coupled to the attenuator234 which reduces it to levels suitable for input to AFE 220 (e.g.,which may be CMOS, for example). The sensed signal is processed by AFE220 similar to how the AFE 138 process the received signal 129. Thedigital feedback circuitry 232 the processes the feedback signal tocompare it to the transmitted signal, which it may receive from thedigital transmit circuitry 158.

In an example implementation, the digital feedback circuitry 232 maycompare the feedback signal to the corrected signal 409 (FIG. 4) toensure they have the same frequency offset. If not, then actions may beperformed such as triggering a recalibration of frequency offsetcorrection circuitry (see e.g., FIG. 6, below), generating an errorflag, and/or the like. If the frequency offset is the same for the twosignals, then the phase offset between the two signals is estimated andcorrected. The phase offset should be fixed since phase noise is thesame for the transmit and feedback paths. Then, a least squareestimation algorithm is performed on the feedback signal to determinedigital predistortion coefficients to be used in the digital transmitcircuitry 154.

In another example implementation, the digital feedback circuitry 232may undo the correction to the feedback signal (i.e., remove the phasecorrection that was applied by digital transmit path 158) and thencompare the feedback signal to the uncorrected signal 419 (FIG. 4) toensure they have the same frequency offset. If not, then actions may beperformed such as triggering a recalibration of frequency offsetcorrection circuitry (see e.g., FIG. 6, below), generating an errorflag, and/or the like. If the frequency offset is the same for the twosignals, then the phase offset between the two signals is estimated andcorrected. The phase offset should be fixed since phase noise is thesame for the transmit and feedback paths. Then, a least squareestimation algorithm is performed on the feedback signal to determinedigital predistortion coefficients to be used in the digital transmitcircuitry 154.

FIG. 3A is a flowchart illustrating an example process forlow-phase-noise reception by a microwave backhaul transceiver.

The process begins with block 302 in which SAW or BAW-based oscillatorsignal 183 is generated by synthesizer 182 based on the output 181 ofresonator 180 which may be a bulk acoustic wave (BAW) or surfaceacoustic wave (SAW) resonator. An advantage of generating the signal 183from a BAW or SAW resonator is that BAW or SAW resonators are typicallyable to achieve much lower phase noise at much higher frequencies thancrystal oscillators. A drawback of using a BAW or SAW resonator,however, is that they tend to have a high temperature coefficient (i.e.,resonant frequency varies substantially over expected range of operatingtemperature). Accordingly, aspects of this disclosure provide forcompensating for phase and/or frequency drift of the SAW OR BAWresonator 180.

In block 304, error signal 185 is generated based on the phasedifference between the SAW OR BAW-based oscillator signal 183 and areference signal (e.g., reference signal 189 in FIG. 1A and FIG. 1B orreference signal 201 in FIG. 2A and FIG. 2B). Example circuitry forgenerating the error signal is described below with reference to FIGS.5A-5C.

In block 306, the synthesizer 182 tunes the frequency of the SAW ORBAW-based oscillator signal 183 based on the error signal 185 generatedin block 304.

In block 308, the received signal is downconverted to baseband using theBAW or SAW-based oscillator signal 183.

In block 310, the digital receive circuitry 142 corrects the phase ofthe baseband signal using the error signal 185 generated in block 304.Example circuitry for performing that phase correction is describedbelow with reference to FIG. 4.

FIG. 3B is a flowchart illustrating an example process forlow-phase-noise transmission by a microwave backhaul transceiver.

The process begins with block 302 in which SAW OR BAW-based oscillatorsignal 183 is generated by synthesizer 182 based on the output 181 ofresonator 180 which may be a bulk acoustic wave (BAW) or surfaceacoustic wave (SAW) resonator. An advantage of generating the signal 183from a BAW or SAW resonator is that BAW or SAW resonators are typicallyable to achieve much lower phase noise at much higher frequencies thancrystal oscillators. A drawback of using a BAW or SAW resonator,however, is that they tend to have a high temperature coefficient (i.e.,resonant frequency varies substantially over expected range of operatingtemperature). Accordingly, aspects of this disclosure provide forcompensating for phase and/or frequency drift of the SAW OR BAWresonator 180.

In block 304, error signal 185 is generated based on the phasedifference between the SAW OR BAW-based oscillator signal 183 and areference signal (e.g., reference signal 189 in FIG. 1 or referencesignal 201 in FIG. 2). Example circuitry for generating the error signalis described below with reference to FIGS. 5A-5C.

In block 306, the synthesizer 182 tunes the frequency of the SAW ORBAW-based oscillator signal 183 based on the error signal 185 generatedin block 304.

In block 328, the digital transmit circuitry 154 (pre)corrects the phaseof the baseband signal using the signal error signal 185 generated inblock 304. Example circuitry for performing that phase correction isdescribed below with reference to FIG. 4.

In block 330, the phase-corrected signal is processed by transmit AFE158 where it is upconverted using the SAW OR BAW based oscillator signal183.

FIG. 4 shows an example implementation of a portion of the transmit andreceive digital circuitry of FIGS. 1 and 2. The phase error signal 185from the auxiliary PLL 184 is multiplied, in multiplier circuit 402, byN (e.g., provided by controller 104), where:

-   -   N=(f_RF−f_IF)/f_Aux, when DPLL sampling rate and accumulator        sampling rate are the same;    -   N=(f_RF−f_IF)/f_Aux×(sampling rate of DPLL/sampling_rate of        accumulator), when DPLL sampling rate and accumulator sampling        rate are not the same    -   f_RF is the frequency of signal 183;    -   f_IF is the frequency of transmit and/or receive signal at        interface 122 a; and    -   f_Aux is the frequency of the reference signal 189 (FIG. 1) or        201 (FIG. 2).        The resulting signal 403 is accumulated in accumulator 412 and        then added, by summer 404, to signal 411 generated by direct        digital frequency synthesizer 410. The frequency of signal 411        is the frequency of the microwave channel to be downconverted        (for receive) or upconverted to (for transmit). Signal 405,        representing a phase angle, θ, is then processed by circuit 406        which outputs cos(θ)+j*sin(θ) as signal 407. Signal 407 is then        multiplied by the baseband signal 419 to generate phase        corrected signal 409.

FIG. 5A shows a first example implementation of the auxiliary PLL ofFIGS. 1 and 2. Divider 502 divides the SAW OR BAW-based oscillatorsignal 183 by a ratio 513 to generate signal 503. Bang bang phasedetector 504 determines the phase difference between signal 503 and thereference signal 189 (FIG. 1) or 201 (FIG. 2) and outputs the phasedifference as signal 505. Signal 505, a digital signal, is filtered byloop filter 506 resulting in signal 507. A gain is applied to signal 507resulting in the error signal 185. Signal 185 is output from the aux PLL184 and is fed back to digital delta-sigma modulator (DSM) 510. DSM 510generates signal 511 which is summed with a nominal value of N (FIG. 4)to generate the divider ratio 513.

FIG. 5B shows a second example implementation of the auxiliary PLL ofFIGS. 1 and 2. ADC 522 digitizes the reference signal 189 (FIG. 1) or201 (FIG. 2) to generate signal 523, which may be a real valued signal.Signal 523 is downconverted to baseband signal 525 by circuit 524.Baseband signal 525 may be a complex valued signal represented byin-phase and quadrature-phase components. Mixer 526 mixes signal 525with signal 533 to generate signal 527, which may be a complex valuedsignal represented by in-phase and quadrature-phase components. Circuit528 converts the I,Q representation to an angle value 529 representingthe phase difference between signals 525 and 533. The angle value 529 isfiltered by loop filter 506 to generate signal 185, which is accumulatedby accumulator 530 to generate signal 531. Circuit 532 converts theangle value 531 to the in-phase and quadrature-phase components ofsignal 533.

FIG. 5C shows a third example implementation of the auxiliary PLL ofFIGS. 1 and 2. ADC 522 digitizes the reference signal 189 (FIG. 1) or201 (FIG. 2) to generate signal 523, which may be a real valued signal.Signal 523 is downconverted to baseband signal 525 by circuit 524.Baseband signal 525 may be a complex valued signal represented byin-phase and quadrature-phase components. Circuit 528 converts the I,Qrepresentation to an angle value 535. The combiner 536 outputs thedifference between the angle 535 and the signal 531 as signal 537. Thesignal 537 is filtered by loop filter 506 to generate signal 185, whichis accumulated by accumulator 530 to generate signal 531.

FIG. 5D shows a fourth example implementation of the auxiliary PLL ofFIGS. 1 and 2. Mixer 550 mixes signal 523, which is the real componentof a digitized version of the reference signal 189 (FIG. 1) or 201 (FIG.2), with signal 565 to generate signal 551, which is filtered by filter552 and then normalized by circuit 556 to generate signal 557. Thefilter 552 is, for example, a narrowband notch filter centered at2×f₁₈₉. Circuit 558 analyzes signal 557 to determine if the real part ofsignal 557 is greater than zero. If not, this sample is skipped. If so,then the imaginary part of signal 557 is conveyed to loop filter 560.Adder 562 adds signal 561 output of loop filter 560 to the value F₁₈₉(FIG. 1) or F₂₀₁ (FIG. 2), where F₁₈₉ is the frequency of signal 189,and F₂₀₁ is the frequency of signal 201. The output of adder 562 isinput to phase error accumulator 564 which outputs the accumulated phaseerror as signal 565. Signal 561 output of loop filter 560 is alsoconveyed to divider 566 which divides it by a divide ratio, which may befixed or variable. The output of divider 566 is input to phase erroraccumulator 568 which outputs the accumulated phase error as signal

FIG. 6 shows a portion of an example microwave backhaul receiver, inaccordance with aspects of this disclosure. The depicted portion of themicrowave transceiver 100 is similar to those described above butcomprises frequency offset correction circuitry 602. Portions ofmicrowave transceiver 100 not shown in FIG. 6 may be as shown in any ofFIGS. 1A, 1B, 2A, 2B, and 2C.

The frequency offset correction circuitry 602 is operable to determine afrequency offset between the signal 183 on the one hand and the signal189 or 201 on the other hand. In an example implementation, thefrequency offset correction circuitry 602 is operable to count thenumber of periods of the signal 183 occurring within a determined numberof cycles of the signal 189 or 201. The count may then be used tocalculate the frequency offset ppm using the expression(C₁₈₃−E₁₈₃)/E₁₈₃λ1e6 ppm where C₁₈₃ is the counted number of clockcycles of 183 and E₁₈₃ is the expected number of clock cycles of signal183. The frequency offset ppm may be calculated by frequency offsetcircuitry 602 and provided to digital transmit circuitry 154 and digitalreceive circuitry 142 as signal 603.

The digital receive circuitry 142 and the digital transmit circuitry 154are operable to receive the frequency offset 603 and use it to estimatethe phase error of the signal 181.

In an example implementation (e.g., where the microwave transceiver 100is required to receive only a single polarization of asingle-input-output signal), the determined frequency offset 603 may besufficient for the digital receive circuitry 142 and the digitaltransmit circuitry 154 to estimate and correct at least part of thephase error. Remaining phase error can be corrected in modem 124.

In another example implementation (e.g., where the microwave transceiver100 is required to receive multiple polarizations and/or amultiple-input-multiple-output signal), the determined frequency offset603 may be insufficient for the digital receive circuitry 142 and thedigital transmit circuitry 154 to obtain a sufficiently accurateestimate of the phase error of the signal 181. Accordingly, thefrequency offset may be used to initially reduce the phase error (e.g.,from on the order of 1000 ppm to on the order of 100 ppm) and thenfrequency correction may be frozen and then the Aux PLL 189 or 201 maybe used as described above to phase lock the frequency corrected signalto the reference signal 189 or 201.

In accordance with an example implementation of this disclosure, asystem comprises a microwave backhaul outdoor unit (e.g., 100) comprisesa first resonant circuit (e.g., 180), phase error determinationcircuitry (e.g., 184), and phase error compensation circuitry (e.g.,182, 142, and/or 154). The first resonant circuit is operable togenerate a first signal (e.g., 181) characterized by a first amount ofphase noise and a first amount of temperature stability. The phase errordetermination circuitry is operable to generate a phase error signal(e.g., 185) indicative of phase error between the first signal and asecond signal (e.g., 189) characterized by a second amount of phasenoise that is greater than the first amount of phase noise, and a secondamount of temperature instability that is less than the first amount oftemperature instability. The phase error compensation circuitry isoperable to adjust the phase of a data signal (e.g., 409) based on thephase error signal, the adjustment resulting in a phase compensatedsignal (e.g., 409). The microwave backhaul outdoor unit may compriseinterface circuitry (e.g., 122 a) operable to receive the second signalfrom a microwave backhaul indoor unit (e.g., 120). The microwavebackhaul outdoor unit may comprise a second resonant circuit (e.g., 188)operable to generate the second signal. The first resonant circuit maybe a surface acoustic wave resonator or a bulk acoustic wave resonator,and the second resonant circuit may be a crystal oscillator. Themicrowave backhaul outdoor unit may comprise local oscillator generationcircuitry (e.g., 182, 168, and/or 140) operable to generate a localoscillator signal (e.g., output of 140) based on the first signal, andanalog front end circuitry (e.g., 138) operable to process a receivedsignal (e.g., 129) to generate the data signal, wherein the generationof the data signal comprises mixing (e.g., by mixer 132) of the receivedsignal with the local oscillator signal. The microwave backhaul outdoorunit may comprise local oscillator generation circuitry (e.g., 182, 168,and/or 140) operable to generate a local oscillator signal (e.g., outputof 168) based on the first signal, and analog front end circuitry (e.g.,158) operable to process the data signal to generate an RF signal (e.g.,167) for transmission, wherein the generation of the RF signal comprisesmixing (e.g., by mixer 164) of the data signal with the local oscillatorsignal. The phase error determination circuitry comprises frequencydivider circuitry (e.g., 502) operable to divide a reference signal(e.g., 183) generated based on the first signal by a determined ratio togenerate a third signal (e.g., 503), and signal processing circuitry(e.g., 504, 506 and 508) operable to generate the phase error signalbased on a phase difference between the third signal and the secondsignal. The phase error determination circuitry may comprise a deltasigma modulator (e.g., 511) operable to control the determined ratiobased on the phase error signal. The phase error compensation circuitrymay comprise: multiplier circuitry (e.g., 402) operable to multiple afrequency of the phase error signal by a determined ratio to generate afourth signal (e.g., 403); frequency synthesizer circuitry (e.g., 410)operable to generate a fifth signal (e.g., 411) at a selected frequency;and summer circuitry (e.g., 404) operable to sum the fourth signal andthe fifth signal to generate a sixth signal (e.g., 405). The determinedratio may be the ratio of the frequency of a reference signal (e.g.,183) generated based on the first signal to the frequency of the secondsignal. The phase compensation circuitry may comprise a phase lockedloop. The microwave backhaul outdoor unit may comprise interfacecircuitry (e.g., 122 a) operable to transmit the phase compensatedsignal (e.g., 409) to a microwave backhaul indoor unit (e.g., 120). Theinterface circuitry may be operable to upconvert the phase compensatedsignal prior to the transmission (e.g., over coaxial cable or fiberoptic cable 144) to the microwave backhaul indoor unit. The system maycomprise a microwave backhaul indoor unit (e.g., 120) operable toreceive the phase compensated signal from the microwave backhaul outdoorunit. The microwave backhaul outdoor unit may comprise frequencysynthesizer circuitry (e.g., 182, 168, and/or 140) operable to generatea reference signal (e.g., 183) based on the first signal. The frequencysynthesizer circuitry may be operable to compensate a phase of thereference signal based on the phase error signal, the compensationresulting in a phase compensated reference signal (e.g., 183). Thefrequency synthesizer circuitry may be operable to generate a microwavefrequency local oscillator signal based on the phase compensatedreference signal.

In accordance with an example implementation of this disclosure, asystem comprises a microwave backhaul outdoor unit comprising: a surfaceacoustic wave or bulk acoustic wave resonator (e.g., 180) operable togenerator a first reference signal (e.g., 181); frequency synthesizercircuitry (e.g., 182, 168, and/or 140) operable to generate a microwavefrequency local oscillator signal (e.g., output of 168 or 140) based onthe first reference signal; crystal oscillator circuitry (e.g., 188)operable to generate a second reference signal (e.g., 189); phase errordetermination circuitry (e.g., 184) operable to generate a signalindicative of a phase error between the first reference signal and thesecond reference signal; and phase error compensation circuitry (e.g.,142, 154, and/or 182) operable to adjust the phase of a signal (e.g.,409 or 183) based on the signal indicative of the phase error.

The present method and/or system may be realized in hardware, software,or a combination of hardware and software. The present methods and/orsystems may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip. Some implementations may comprise a non-transitorymachine-readable (e.g., computer readable) medium (e.g., FLASH drive,optical disk, magnetic storage disk, or the like) having stored thereonone or more lines of code executable by a machine, thereby causing themachine to perform processes as described herein.

While the present method and/or system has been described with referenceto certain implementations, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted without departing from the scope of the present methodand/or system. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the presentdisclosure without departing from its scope. Therefore, it is intendedthat the present method and/or system not be limited to the particularimplementations disclosed, but that the present method and/or systemwill include all implementations falling within the scope of theappended claims.

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, circuitry is “operable” to perform a function wheneverthe circuitry comprises the necessary hardware and code (if any isnecessary) to perform the function, regardless of whether performance ofthe function is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, etc.).

What is claimed is:
 1. A system comprising: a microwave backhaul outdoorunit comprising: a first resonant circuit operable to generate a firstsignal characterized by a first amount of phase noise and a first amountof temperature stability; phase error determination circuitry operableto generate a phase error signal indicative of phase error between saidfirst signal and a second signal, wherein said second signal ischaracterized by a second amount of phase noise that is greater thansaid first amount of phase noise, and said second signal ischaracterized by a second amount of temperature instability that is lessthan said first amount of temperature instability; phase errorcompensation circuitry operable to adjust the phase of a data signalbased on said phase error signal, said adjustment resulting in a phasecompensated signal.
 2. The system of claim 1, wherein said microwavebackhaul outdoor unit comprises interface circuitry operable to receivesaid second signal from a microwave backhaul indoor unit.
 3. The systemof claim 1, wherein said microwave backhaul outdoor unit comprises asecond resonant circuit operable to generate said second signal.
 4. Thesystem of claim 3, wherein: said first resonant circuit is a surfaceacoustic wave resonator or a bulk acoustic wave resonator; and saidsecond resonant circuit is a crystal oscillator.
 5. The system of claim1, wherein said microwave backhaul outdoor unit comprises: localoscillator generation circuitry operable generate a local oscillatorsignal based on said first signal; and analog front end circuitryoperable to process a received signal to generate said data signal,wherein said generation of said data signal comprises mixing of saidreceived signal with said local oscillator signal.
 6. The system ofclaim 1, wherein said microwave backhaul outdoor unit comprises: localoscillator generation circuitry operable generate a local oscillatorsignal based on said first signal; and analog front end circuitryoperable to process said data signal to generate an RF signal fortransmission, wherein said generation of said RF signal comprises mixingof said data signal with said local oscillator signal.
 7. The system ofclaim 1, wherein said phase error determination circuitry comprises:frequency synthesizer circuitry operable to generate a reference signalbased on said first signal; frequency divider circuitry operable todivide said reference signal by a determined ratio to generate a thirdsignal; and signal processing circuitry operable to generate said phaseerror signal based on a phase difference between said third signal andsaid second signal.
 8. The system of claim 7, phase error determinationcircuitry comprises a delta sigma modulator operable to control saiddetermined ratio based on said phase error signal.
 9. The system ofclaim 1, wherein said phase error compensation circuitry comprises:multiplier circuitry operable to multiple a frequency of said phaseerror signal by a determined ratio to generate a third signal; frequencysynthesizer circuitry operable to generate a fourth signal at a selectedfrequency; and summer circuitry operable to sum said third signal andsaid fourth signal to generate a fifth signal.
 10. The system of claim9, wherein said determined ratio is the ratio of the frequency of areference signal generated based on said first signal to the frequencyof the second signal.
 11. The system of claim 1, wherein phasecompensation circuitry comprises a phase locked loop.
 12. The system ofclaim 1, wherein said microwave backhaul outdoor unit comprisesinterface circuitry operable to transmit said phase compensated signalto a microwave backhaul indoor unit.
 13. The system of claim 12, whereinsaid interface circuitry is operable to upconvert said phase compensatedsignal prior to said transmission to said microwave backhaul indoorunit.
 14. The system of claim 13, wherein said transmission of saidphase compensated signal is over a coaxial cable or fiber optic cable.15. The system of claim 1 comprising a microwave backhaul indoor unitoperable to receive said phase compensated signal from said microwavebackhaul outdoor unit.
 16. The system of claim 13, wherein said indoorunit is communicatively coupled to said microwave backhaul outdoor unitvia a coaxial cable or fiber optic cable.
 17. The system of claim 1wherein said microwave backhaul outdoor unit comprises frequencysynthesizer circuitry operable to generate a reference signal based onsaid first signal.
 18. The system of claim 17 wherein said frequencysynthesizer circuitry is operable to compensate a phase of saidreference signal based on said phase error signal, said compensationresulting in a phase compensated reference signal.
 19. The system ofclaim 18, wherein said frequency synthesizer circuitry is operable togenerate a microwave frequency local oscillator signal based on saidphase compensated reference signal.
 20. A system comprising: a microwavebackhaul outdoor unit comprising: a surface acoustic wave or bulkacoustic wave resonator operable to generator a first reference signal;frequency synthesizer circuitry operable to generate a microwavefrequency local oscillator signal based on said first reference signal;crystal oscillator circuitry operable to generate a second referencesignal; phase error determination circuitry operable to generate asignal indicative of a phase error between said first reference signaland said second reference signal; and phase error compensation circuitryoperable to adjust the phase of a signal based on said signal indicativeof said phase error.